1. Field of the Invention
The present invention relates to a semiconductor device, a method for making the same, and to an electronic device utilizing the semiconductor device.
2. Description of the Related Art
In recent years, various wire-bond-type chip size packages (CSPs) have appeared in response to multi-electrode trends of semiconductor chips. Among the different types of CSPs, FIG. 7A shows a flexible printed circuit (FPC) type CPS. The FPC type CPS comprises a base a composed of a polyimide resin, and wiring films b composed of a metal such as copper formed on the surface of the base a. Holes c for forming electrodes (herein after referred to as xe2x80x9celectrode-forming holes cxe2x80x9d) are formed in the base a, and fine spherical electrodes d composed of solder are formed in the electrode-forming holes c. A semiconductor chip f placed on the base a is bonded to the base a with a silver-paste film e. Gold bonding wires g connect electrodes of the semiconductor chip f with the corresponding wiring films b. The semiconductor chip f and the bonding wires g are sealed with a sealing resin h.
FIG. 7B shows a rigid substrate type CPS. The rigid substrate type CPS comprises a rigid wiring substrate i having holes (through-holes) j for forming electrodes (hereinafter referred to as electrode-forming holes), wiring films k formed on the rigid wiring substrate i, and wiring films l. The wiring films l are connected to the wiring films k, functions as an external electrode, and do not require solder spherical electrodes. A semiconductor chip f is placed on an insulating film m composed of a resist between the wiring films k, and is bonded to the insulating film m with a silver-paste film e. Gold bonding wires g connect electrodes of the semiconductor chip f with the corresponding wiring films k. The semiconductor chip f and the bonding wires g are sealed with a sealing resin h.
Although the FPC type CPS shown in FIG. 7A has an advantage of a high rate of heat dissipation, it does not allow electroplating since fine solder spherical electrodes are in the wiring films b which are electrically isolated from each other. Thus, it is significantly difficult to form fine solder spheres. Since it is impossible to reduce the diameter of the electrode-forming holes c, reduction in the array pitch between the hole-electrodes is limited. Accordingly, the appearance of the electrode-forming holes and of the spherical electrodes is inferior. Since the wiring films b are formed by selective etching, production of a fine pattern is limited. Furthermore, the base a is flexible; hence workability is inferior and production of large devices is difficult.
Although the rigid substrate type has an advantage that no solder spherical electrode is formed, it is difficult to reduce the diameter of the electrode-forming holes to 0.35 mm or less. This is a factor limiting higher integration of semiconductor devices. Furthermore, production of a fine wiring film pattern is difficult, the appearance of the electrode-forming holes is inferior, and heat dissipation is slow. Since the electrode-forming holes are formed by drilling, production is difficult.
It is an object of the present invention to provide a CSP- or BGA-type semiconductor device that allows mounting of fine spherical electrodes.
It is another object of the present invention to provide a CSP- or BGA-type semiconductor device that achieves miniaturization of electrode-forming holes, fineness of a wiring film pattern, improved appearance, and simplified production process.
A first aspect of the present invention is a semiconductor device comprising: a plurality of wiring films formed on a front surface of a base comprising an insulating resin and having electrode-forming holes, the surfaces of the wiring films and the surface of the base being positioned on the same plane and at least parts of the wiring films overlapping with the electrode-forming holes; a conductive material embedded into the electrode-forming holes to form external electrodes on the back surface, away from the wiring films, of the base; a semiconductor element positioned on the front surface of the base with an insulating film therebetween, the back surface of the semiconductor element being bonded to the front surface of the base; and wires for bonding the electrodes of the semiconductor element to the corresponding wiring films.
Since the wiring films are formed on a front surface section of the base so as to embed them; surface steps are not formed. Since a semiconductor device is mounted onto the surface, bonding of the semiconductor device and wire bonding are readily performed, resulting in enhancing reliability of the semiconductor device. Since the electrode-forming holes are formed by exposure and development of the base, fineness and high integration permitting large-scale integration and multi-electrodes of the semiconductor device can be achieved.
A metal ring may be bonded on the front surface of the base at the exterior of the connecting sections with wires in the wiring films. In such a preferred embodiment, the ring is used as an electrical power source, for example, a ground source, as an electrostatic shield for electrostatically shielding between the semiconductor device and the exterior, and as a dam for preventing leakage of the sealing resin to the exterior.
A second aspect of the present invention is A method for making a film circuit comprising: a step of forming wiring films on a metal film for stopping etching as an underlying layer by plating using a mask film, the mask being selectively formed on a front surface of a metal substrate; a step of forming a base comprising an insulating resin and having electrode-forming holes on the front surface of the metal substrate such that at least parts of the wiring films are partly exposed; and a step of etching at least the region of the metal substrate, in which the wiring films are formed, from the back surface until the metal film for stopping etching is exposed.
Since the electrode-forming holes can be formed by patterning of the insulating resin on the metal substrate, fineness of the electrode-forming holes can be achieved. Thus, the diameter of the electrode-forming holes can be reduced to 0.22 mm or less, whereas the lower limit of the diameter is 0.25 mm for a conventional FPC type, or 0.35 mm for a rigid substrate type. Such fineness of the electrode-forming holes can increase the array density of the electrode-forming holes. The electrode-forming holes can be formed by patterning the insulating resin with a reduced working load and increased productivity compared with the formation of electrode-forming holes by drilling as in the rigid substrate type.
Preferably, the metal film for stopping etching is deposited on the surface of the metal substrate; a mask film is selectively formed on the metal film for stopping etching, and the wiring films are formed on the metal film as an underlying layer through the mask film by plating; and after completing the etching step for exposing the metal film for stopping etching from the back surface at least in the region of the metal substrate in which the wiring films are formed, the metal film for stopping etching is removed.
The region, in which at least wiring films are formed, of the metal substrate is etched from the back surface so that the underlying metal film for etching stop is exposed and the metal substrate remains as a ring at the exterior. Thus, the remaining section can be used as a ring. The ring can be used as a ground electrical source terminal and an electrostatic shield, as described above. Since the ring forms an outer shape of the semiconductor device and is formed by etching, working accuracy can be increased. Thus, the semiconductor device has high shape accuracy.
Since it is produced using a metal substrate as a mother material, deformation such as distortion will not occur during the production. Thus, working is easy. A large semiconductor device, therefore, can be readily formed.
A third aspect of the present invention is an electronic device comprising a semiconductor device comprising: a plurality of wiring films formed on a front surface of a base comprising an insulating resin and having electrode-forming holes, the surfaces of the wiring films and the surface of the base being positioned on the same plane and at least parts of the wiring films overlapping with the electrode-forming holes; a conductive material embedded into the electrode-forming holes to form external electrodes on the back surface, away from the wiring films, of the base; a semiconductor element positioned on the a front surface of the base with an insulating film therebetween, the back surface of the semiconductor element being bonded to the front surface of the base; and wires for bonding the electrodes of the semiconductor element to the corresponding wiring films.